REGENERATION 



311 



In an early embryo when an embryonic field is extirpated, there is generally no regener- 

 ation. This means that at this stage regeneration as a property of the embryo is re- 

 stricted to local fields, and is not related to "the organism as a whole". 



There is still a great deal of room for further study of regeneration, particularly as it 

 may be affected by mitotic inhibitors, colchicine, dinitrophenols, specific ions, pH, 

 temperature, light (where pigment cells are involved). 



Fig. 1. A larva showing the stage in which 

 the right fore limb was amputated. 

 The double pointed arrow indicates the 

 level of amputation. 



Figs. 2 and 3. Larvae which were given a 

 single exposure to x-rays immediately 

 after limb amputation. Limb regener- 

 ation has been completely suppressed. 



Figs. 4 and 5. Control larvae showing the 

 progress of normal regeneration 12 and 

 25 days after limb amputation. Stip- 

 pling on the limb stump in Figure 4 

 indicates the approximate extent of the 

 normal regeneration blastema on the 

 twelfth day. 



Figs. 6 and 7. Larvae which were given a 

 single exposure to x-rays on the twelfth 

 day after limb amputation. A blastema 

 was present at the time of radiation, as 

 shown by stippling. Limb regeneration 

 was completely suppressed. 



(From Butler G Puckctt 1940: 

 Jour. Exp. Zool. 84:223) 



doys 



Recent experiments have shown that the proximo-distal polarity of a Urodele limb can be 

 reversed and the regeneration of distal structures obtained from the original proximal 

 end of a limb. Such experiments, which are relatively easy to perform (Butler, 1955; 

 Deck, 1955), involve amputation of a forelinib at the wrist level and insertation of the 

 cut end into a pocket made in the body wall posterior to the shoulder region; later the 

 lin:ib is amputated above the elbow and the upper arm then becomes the free end of the 

 transplanted limb. Such linnbs regularly become innervated either by the brachial 

 plexus or by spinal nerves posterior to the plexus. After innervation of the reversed 

 limb has taken place, a blastema forms at the tip of the limb (its original proximal end) 

 and develops into a wrist and digits. In this type of regenerative activity the interrela- 

 tions between the blastema and the formed structures of the limb beneath it are of par- 

 ticular interest. 



